1. Field of the Invention
The present invention relates to a pattern data processing apparatus for incorporation in integrated services of digital network (so-called "Information Network System) for displaying desired graphics patterns on a monitor image display based on data transmitted via a digital communication line.
2. Description of the Prior Art
Where a process is to be performed for displaying a graphics pattern based on pattern information such as vertex information on a polygon transmitted via a digital communication line and for shading an internal portion of the pattern, it is necessary to detect a closed area in the pattern. There are known two processes for detecting such a closed area.
The first process requires a memory for storing all information on the shape of a given graphics pattern. The second process needs no memory and searches for a closed area based on information as to the intersections of a given pattern. With the first process, since information on the closed area is stored in the memory, the process can employ various types of shading (shading over the full surface, vertical hatching, horizontal hatching, cross-hatching, slant hatching) and various processing directions (downward, rightward, etc.). However, the memory is required to have quite a large capacity as it has to store all pattern information given.
According to the second processes, received vertex information items are sequentially connected to find a straight line, then an intersection of the straight line and a scanning direction, and the closed area is shaded using the intersection information. Although the second process requires no memory, a program for performing the process is complex and the time required for effecting the process is long. Since complicated processing such as crosshatching is difficult to achieve, the types of processing that can be accomplished are limited.